JP2004-9891A discloses a vehicle occupant protection device described in an opening paragraph. In the vehicle occupant protection device disclosed in the document, the amount of the forward movement of the headrest is determined according to the magnitude of the relative speed between a bumping vehicle and a bumped vehicle or the amount of distortion so as to correspond to the amount of the backward movement of the head of the occupant at the time of the crash.
However, according to such prior art, since the distance between the headrest and the occupant's head is not considered in determining the amount of the forward movement of the headrest, the determined amount of the forward movement of the headrest can be inadequate depending on the distance between the headrest and the occupant's head, thereby failing to appropriately protect the occupant.